News Release Number: STScI-1990-23

The Hubble Reveals the Evolving Core of a Dense Star Cluster

January 16, 1991: Astronomers today presented pictures taken with the Hubble Space Telescope of the heart of M15, a dense cluster of stars within our own Galaxy. The pictures show for the first time that M15 is in the process of recovering from a deep implosion of its core regions, caused by a massive gravitational instability. Many other star clusters may have experienced a similar collapse, in which their central stars crowd into a compact aggregate, causing a sharp rise in central density. This process may also happen in the dense centers of galaxies, where it may lead to the formation of massive black holes. The analysis of the Hubble images was presented by Dr. Tod R. Lauer of the National Optical Astronomy Observatories, Tucson, Arizona, Dr. Jon A. Holtzman of Lowell Observatory, Flagstaff, Arizona, Dr. Sandra M. Faber of Lick Observatory, Santa Cruz, California, and fellow members of the Hubble Wide Field/Planetary Camera imaging team, at the American Astronomical Society meeting in Philadelphia, Pennsylvania.